This invention relates to a silver halide photographic emulsion and more particularly to a silver halide photographic emulsion used for high speed roomlight handling light-sensitive materials.
Recently, improvement in efficiency of reversing operation has been desired in the field of printing due to complexity of prints, development of scanners, etc. For this purpose, photographic films extremely low in sensitivity, namely, about 10.sup.-4 -10.sup.-5 of that of the conventional reversal film have been developed and these have began to be practically used as reversal films which can be handled under roomlight (under white fluorescent lamp excluding ultraviolet ray), namely, as roomlight handling light-sensitive materials. Properties required for such roomlight handling light-sensitive materials are that they can provide hard tone and sufficient maximum density, they can be handled under roomlight for a long time and they have a high sensitivity to the light sources of printers. However, conventional roomlight handling light-sensitive materials are not satisfactory in these properties.
Generally, such extremely low sensitivity photographic emulsions as can be utilized as roomlight handling light-sensitive materials can be obtained by using inorganic desensitizers such as rhodium salts or organic desensitizers such as pinakryptol yellow. For example, there have been methods for making roomlight handling light-sensitive materials with use of a large amount of rhodium salts (see Japanese Patent Unexamined Publications (Kokai) No. b 125734/81, No. 149030/81, No. 190943/83, etc.). According to these methods a rhodium salt is used in silver halide emulsion mainly composed of silver chloride in an amount to reduce the sensitivity of the emulsion about 1/300-about 1/500. However, silver chloride emulsions depressed in their sensitivity with rhodium salts are liable to cause fog when handled under roomlight and especially the fog conspicuously increases with increase in sensitivity.
The invertors have confirmed that when a silver halide emulsion which has nearly the same sensitivity as the above mentioned extremely low sensitivity silver halide emulsions mainly composed of silver chloride and prepared using a rhodium salt is prepared using an organic desensitizer, there can be obtained roomlight handling light-sensitive materials free from the defects caused by use of rhodium salts. However, it has also been found, that the silver halide emulsions prepared using organic desensitizers can provide hard tone and high maximum density because they are mainly composed of silver chloride, but on the other hand they have the new problem that conspicuous decrease in sensitivity occurs during the period from imagewise exposure to development when they are under roomlight condition. There have been various methods proposed to solve this problem (e.g., Japanese Patent Applications No. 31413/83, No. 33600/83, No. 54536/83, No. 39413/84), but according to these methods the problem has not yet been completely solved.